In recent years, photocatalytic fine particles using titanium dioxide are attracting attention as an environmental cleaning material for antimicrobial, deodorization, antifouling, air cleaning, water cleaning and the like. The photocatalytic mechanism of titanium dioxide is considered attributable to the following mechanism. Upon irradiation of light on a titanium dioxide fine particle, an electron and a hole are generated inside the titanium dioxide fine particle, which reacts with water or oxygen in the vicinity of the surface of a titanium dioxide fine particle to generate hydroxy radical or hydrogen peroxide. As a result, strong oxidation reduction activity of this hydroxy radical or hydrogen peroxide, harmful organic substances are decomposed into carbon dioxide and water, and thereby cleaned. Such photocatalytic activity of a titanium dioxide fine particle is thought to semipermanently continue as long as a titanium dioxide fine particle, light, water and oxygen are present.
By taking advantage of this photocatalytic property of titanium dioxide, as a representative application example, titanium dioxide fine particles are being kneaded into an easily handleable medium, such as fiber or a plastic molded article, or into a coating on the surface of a substrate, such as cloth or paper. However, decomposition or deterioration by the strong photocatalytic activity of titanium dioxide readily occurs not only on harmful organic materials or environmental pollutants but also on the medium itself such as fiber, plastic or paper and this is an obstacle to durability in practical use. Due to easy handleability of the titanium dioxide fine particle, a coating material comprising a mixture of titanium dioxide fine particles and a binder has been developed. However, an inexpensive binder having durability sufficiently high to overcome, for example, decomposition or deterioration on the medium has not yet been found.
JP-A-9-225319 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-9-239277 disclose means for preventing and suppressing the deterioration of a resin medium or the deterioration of a binder due to the strong photocatalytic activity of titanium dioxide particles. The proposed means is a method of allowing a photo-inactive compound having such as aluminum, silicon and zirconium to be supported on a titanium dioxide particle in an archipelago shape having a steric barrier to retard the photocatalytic activity. According to this method, the photo-inactive compound is supported in an archipelago shape; however, specific sites of the resin medium or the binder disadvantageously remain present under the strong photocatalytic activity of titanium dioxide.
JP-A-10-244166 proposes a photocatalytic titanium dioxide obtained by coating a porous calcium phosphate on the surface of titanium dioxide. However, in this case, the photocatalytic activity disadvantageously decreases due to the coated calcium phosphate layer.
International Publication WO99/33566 discloses a powder material of titanium dioxide fine particles, where a porous coating layer of calcium phosphate is formed on at least a part of the surface of a titanium dioxide fine particle and an anionic surfactant is present at the interface therebetween.
With respect to a slurry containing titanium dioxide having photocatalytic activity, JP-A-10-142008 discloses an anatase-type titanium oxide-containing slurry which is obtained by heat-treating a titania sol, a titania gel form or a titania sol-gel mixture in a closed vessel simultaneously with a pressurization treatment and then dispersing using an ultrasonic wave or stirring the treated product.
JP-A-11-343426 discloses a photocatalytic coating material having excellent dispersion stability and specifically discloses a photocatalytic coating material containing, in a solvent, a silica sol and titanium oxide having a Raman spectrum peak in the range of 146 to 150 cm−1 and being occupied by anatase type titanium dioxide in a ratio of 95% by mass or more.
Conventional techniques heretofore proposed cannot provide an industrially useful method for producing a photocatalytic powder material or slurry which can satisfy all of the photocatalytic activity, when used in combination with an organic material, durability and dispersion stability.
In view of these conventional techniques, an object of the present invention is to provide a photocatalytic powder material, a slurry containing the photocatalytic powder, an organic polymer composition containing the photocatalytic powder, a molded article of the organic polymer composition, a coating agent containing the slurry and a structure having provided on the surface thereof the organic polymer composition or the coating agent that can effectively and profitably perform removal of malodor, decompositional removal of harmful substances or pollutants in air, water draining or cleaning treatment, or disinfectant or antifungal action (hereinafter collectively called “environmental cleaning activity”) and at the same time, have high dispersion stability, and therefore, be greatly enhanced in the industrial utility.
Particularly, the present invention provides a photocatalytic powder and a photocatalytic slurry, which can exhibit excellent photocatalytic activity, durability and dispersion stability when coated on the surface of fiber, paper or plastic material, kneaded into such a material, or used for a coating composition.